1. Field of the Invention
The invention relates to the field of magnetic disk drive systems and, in particular, to testing performance of a magnetic disk prior to installation in a disk drive system.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders that include read and write heads. An actuator/suspension arm holds the slider above a magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the slider to fly a particular height above the magnetic disk. The height at which the slider flies depends on the shape of the ABS. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read head and the write head over selected tracks of the magnetic disk.
The magnetic disk includes data regions and servo regions. The servo regions are used to provide sector information, timing information, positioning information, etc. For example, as the magnetic disk makes a revolution, the read head passes over burst fields in the servo regions. The signal read from the burst fields may be used to generate a timing signal. The signal read from the burst fields may also be used to generate a quadrature signal that is used for centering the read head and write head over the center of a track. The information read from the servo regions may be generally referred to as servo data. The servo data is feed back to a control system, which controls the VCM, the rotational speed of the magnetic disk, etc.
One factor that contributes to the effective reading and writing by the slider is the spacing of the read/write heads in relation to the surface of the magnetic disk. The spacing between the read/write heads generally depends on the fly height of the slider, which is determined by the ABS of the slider. As areal densities of magnetic disks increase, it becomes more important to precisely control spacing of the read/write heads in relation to the magnetic disk, as the spacing may be 10 nanometers or less.
To assist in the spacing between the read/write heads and the magnetic disk, some sliders include heating elements that are fabricated proximate to the read/write heads. The read/write heads are fabricated from materials that have a different thermal rate of expansion than the body of the slider. Thus, when an electrical current is applied to the heating elements, the read/write heads protrude from the ABS of the slider. The protrusion causes the read/write heads to extend toward the surface of the magnetic disk, thereby reducing the spacing between the read/write heads and the magnetic disk. The use of heating elements (sometimes referred to as Thermal Fly-Height Control) allows for more precise spacing between the read/write heads and the magnetic disk.
Before being installed in a disk drive, however, magnetic disks are tested to ensure their operability within various disk drives. Generally, the magnetic disks are manufactured in batches and a portion of each batch is tested to evaluate the performance of the magnetic disks before being installed within the disk drives. A test bed simulates operating conditions for the magnetic disks within a disk drive by reading from and writing to the magnetic disks with a slider. Accurate testing is important because it determines whether a batch of disks will meet the specifications of a particular disk drive selected for magnetic disk installation.
Different disk drives, however, may have different sliders with different characteristics (e.g., soft error rates, signal to noise ratios, magnetic track widths, etc.). Accordingly, magnetic disks are tested to determine whether they are suitable for a particular disk drive. The testing also provides a direction for future magnetic disk development. In addition to having accurate magnetic disk testing, it is generally desirable to test the magnetic disks in a relatively rapid manner so as to be more integral to the assembly process (e.g., improved availability of sputtering tools). Accuracy and speed of magnetic disk testing are generally competing interests. For example, due to the large number of magnetic disks in a developed batch, the test bed is usually configured with a single slider to rapidly test the magnetic disks. However, results of a particular magnetic disk may vary from test to test. To address these variations, multiple tests are usually performed with the single slider and the results are then averaged out to provide a statistical recording characteristic of the magnetic disk batch. Even so, the magnetic disk tests are generally slider dependent. Thus, when a magnetic disk is installed, a disk drive configured with a different slider may perform differently than the test bed. These problems may be overcome by using multiple sliders in the test bed, but this generally consumes more time due to the delicate swapping in and out of sliders for different disk drive simulations. Accordingly, there is a need for improved testing that is both accurate and relatively quick.